1. Field of the Invention
The present invention relates to drilling and completing open hole well bores in soft producing zones or formations.
2. Description of the Prior Art
Well bores drilled in soft sandstone, carbonate and the like producing zones or formations are generally completed open-hole, i.e., without a casing or liner installed therein. Special drilling fluids referred to in the art as “drill-in fluids” are used to drill such well bores to minimize the damage to the permeability of the producing zones or formations. A particularly suitable such drill-in fluid used heretofore consists essentially of water, a gelling agent and calcium carbonate. The drill-in fluid forms a filter cake on the walls of the well bore which prevents or reduces fluid loss during drilling, and upon completion of the drilling, stabilizes the well bore during subsequent completion operations such as placing a gravel pack in the well bore.
After the completion operation in the well bore has been accomplished, the filter cake remaining on the walls of the well bore must be removed. This can be accomplished by contacting the filter cake with an aqueous acid solution. However, the use of an aqueous acid solution is hazardous to personnel and often causes tubular goods and the like to be corroded. Also, the aqueous acid solution can react rapidly at the initial point of contact with the well bore thereby creating a fluid loss zone into which the rest of the acid is lost leaving much of the filter cake untouched and in place.
Thus, there are needs for improved clean-up solutions for removing calcium carbonate containing filter cake from open hole well bores.